A Study On The Hydrogen Production Characteristics Of Exhaust Gas-Fuel Reforming In Fixed Bed Reactor

Reformed exhaust gas recirculation（REGR）,which can generate onboard hydrogen-rich gas via catalytic reforming of fuel and engine exhaust gas,is an attractive way to utilize the exhaust gas heat and improve the emissions characteristics of the marine engine fueled with liquefied natural gas.The hydrogen production process of exhaust gas-fuel reforming directly affects the hydrogen content in the reformate,and then affects the performance of marine LNG engine.Therefore,based on the characteristics of marine LNG engine exhaust gas,the hydrogen production characteristics of exhaust gas-fuel reforming with Ni/Al₂O₃ catalyst were investigated by a fixed bed catalytic reforming device in the present study.Firstly,the differences of the morphology,structure and compositions between the original catalyst,the reduced catalyst and the exhaust gas-fuel reformed catalyst were explored by SEM,TEM,XRD,and TGA,respectively.Secondly,the effects of temperature,the molar ratio of CH₄/O₂ or H₂O/CH₄ on partial oxidation reforming and steam reforming of methane were studied by fixed bed catalytic reforming device.Finally,the effects of different temperature,feed ratio and gas hourly space velocity（GHSV）on hydrogen production characteristics of exhaust gas-fuel reforming were studied based on the characteristics of marine LNG engine exhaust gas.The main conclusions obtained are as follows:（1）The results of catalyst characterization show that the main components of the original catalyst are NiO/Al₂O₃ and the carrier Al₂O₃ is fibrous crystal structure.The surface roughness of the catalyst is large and the dispersion of the active metal is good.After the reduction,the main component of the catalyst is Ni/Al₂O₃,while there is a small amount of NiO.The agglomeration of nickel metal particles on the surface of catalyst is observed after exhaust gas-fuel reforming.In addition,TGA analysis shows that there is a small amount of coke deposit on the catalyst after exhaust gas-fuel reforming.（2）The results of partial oxidation reforming and steam reforming of methane show that with the increase of temperature,the volume fractions of H₂ and CO,methane conversion and hydrogen yield increase gradually,the volume fraction of CO₂ increases first and then decreases,while the H₂/CO volume ratio decreases gradually.With the increase of the molar ratio of CH₄/O₂ or H₂O/CH₄,the volume fraction of H₂ increases first and then decreases,and the volume fraction of CO decreases,while the methane conversion,hydrogen yield and H₂/CO volume ratio increase continuously.The difference is that on the partial oxidation reforming process,the volume fractions of CO₂ decreases gradually,while on the steam reforming reaction,the volume fraction increases first and then decreases.（3）The results of exhaust gas-fuel reforming test of marine LNG engine show that as the temperature increases,H₂ and CO volume fractions,methane conversion rate and hydrogen yield increase,while the H₂/CO volume ratio decreases,which is consistent with the single reforming reaction.With the increase of the molar ratio of CH₄/O₂,the volume fraction of H₂ increases and then tends to be flat.The volume fraction of CO and the hydrogen yield increase first and then decrease,while the methane conversion rate decreases continuously.As the molar ratio of H₂O/CH₄increases,the volume fractions of H₂ and CO,methane conversion and hydrogen yield increase first and then decrease,while the H₂/CO volume ratio increases.the volume fraction of H₂ in exhaust gas-fuel reforming reaches peak value of 12.44%when the temperature is 402,the GHSV is 4000h^-1,the molar ratio of CH₄/O₂ is 3 and the molar ratio of H₂O/CH₄ is 2.With the increase of GHSV,the volume fraction of H₂ increases first and then decreases,the volume fraction of CO increases,while the H₂/CO volume ratio decreases gradually.As the GHSV increases,the hydrogen yield increases first and then decreases,while the methane conversion remains constant.As a result,the GHSV shows little influence on the hydrogen production characteristics of exhaust gas-fuel reforming.